Method and apparatus for amplifying radiofrequency currents



Jan. 17, 1933. J. M. AVERY 1,894,578

METHOD AND APPARATUS FOR AMPLIFYING RADIOFREQUENCY CURRENTS Filed July13, 1925 2 Sheets-Sheet 2 A TTORNEY.

Patented Jan. 17, 1 933 UNETED S l A TES PATENT QFFEE JOHN IvI. AVERY,03E FLUSHING, NEW YGRK, ASSIGNOR, BY MESNE ASSIGNMENTS, TO EAIJIOCGBEORATIGIJ OF AMERICA, is CORPORATION OF DELA'W'ARE IIIETHOD ANDAPYARATUS FOR .AIViPLZ A nlication filed Jul 13,

This invention relates to the amplification of radio frequency currents,such as, for eX ample, in radio telephone and telegraph sys tems.

In the operation of radio frequency amplifiers particularly at thehigher frequencies, there is always present a tendency toward localoscillation in one or more of the ampli fier stages. Heretofore variousattempts have been made to prevent such local and objectionableoscillations, but such attempts have usually resulted in eithercomplication of de ices or dilficulty of adjustment, or if free fromsuch local or objectionable oscillations, a uniform maximum transfer andamplification of energy at all the frequencies within its range wasimpossible. Variation in the amplifying power of the radio frequencyamplifier also has not been satisfactorily accomplished heretofore bysimple means.

An object of this invention is to provide an improved method andapparatus for sum plifying electric currents at radio frequencies, whichwill permit of uniform and maximum transfer of energy between saidstages without oscillation in any of the same; and which will permit ofa selective variation in the amplifying power of the system.

A further object is to provide an improved apparatus for accomplishingeach and all of the above objects which will be relatively simple andinexpensive in construction; which may be operated, either with the samenumber of controls as already existing in similar sets, or with aminimum of additional controls; and with which amplification of theradio frequency currents may be obtained without distortion.

Various other objects and advantages will be apparent from the followingdescription of several embodiments of the invention, and the novelfeatures will be particularly pointed out hereinafter in connection withthe ap pended claims.

In the accompanying drawings:

Fig. 1 is a circuit diagram illustrating a receiving circuit for aportion of a radio telephone and telegraph system and employing radiofrequency amplification for the incom- FYING RADIOFREQUENCY CURRENTS1925. Serial No. 43,103.

ing signals, the control of the amplification being in accordance withthis invention;

Fig. 2 is a similar circuit diagram, with the exception that thethermionic relays are inductively coupled instead of being coupled by animpedance as in the preceding figure;

Fig. 3 is a diagram illustrating a circuit arrangement similar to Fig. 1and including two stages of radio frequency amplification, with theamplifying power of the system controlled in accordance with theinvention;

Fig. 4 is a similar diagram, but illustrating a modification of theinvent-ion in the manner of controlling the amplifying power of thesystem;

Fig. 5 is another and similar diagram, but illustrating still anothermanner of controlling the amplifying power of the system; and

Fig. 6 is a circuit diagram of a portion of a radio telephone andtelegraph receiving system employing two stages of radio frequencyamplification, coupled by tuned impedance and with oscillationsprevented in accordance wtih this invention, the system having but asingle additional control for both stages of amplification.

Referring particularly to Fig. l in which is illustrated an applicationof the invention in simple form, the antenna 1 and its inductance 2 maybe tuned by a suitable variable condenser 3, and grounded by a lead l.The antenna circuit is coupled or connected to a three-electrodethermionic valve or relay 5 in the usual or any suitable manner.

The relay 5 is coupled to a second and similar relay 6 by a tunedimpedance, the con nections of which are as follows :The plate of thevalve or relay 5 is connected by a wire 7 to one side of a preferablyvariable condenser 8, the other side of the condenser being connected bya wire 9 to one end of a grid inductance 10 which is tuned by a variablecondenser 11, the inductance and condenser being connected to thefilament circuit 12 by a conductor 13. The two condensers 8 and 11 maybe separately operated, or coupled, in any suitable manner, forconcomitant operation as shown in Fig. 1. One end of the inductance 10is connected by a wire 14 to the grid of the relay 6.

The filament circuit is supplied with energy from a suitable energysource 15 in the usual manner, and a B or plate battery 16 is connectedat one side to the filament circuit as usual in the art and at its otherside by a wire 17 to the wire 7 leading to the plate of the relay Animpedance 18, such as a resistor element or choke winding is in seriesin the conductor 17, so that the B or plate battery 16 may impress acontinuous potential upon the plate of the relay 5. The impedance 18holds back the radio frequency currents thereby forcing the latter totravel through the condenser 8 and the rest of the plate circuit. The Bor plate battery 16 may be also employed as a source of energy for theoutput circuit of the relay 6. It will be understood that either theinductance 10 or capacity 11 may be made variable in order to obtain aprope tuning of the impedance coupling.

In the operation of the system of radio frequency amplification justdescribed, the input currents entering the relay 5, either from apreceding relay or from the antenna circuit, will be amplified, andimpressed upon the grid of the next successive relay 6. The battery 16will 1 aintain a continuous potential upon the plates of the relays 5and 6, the exact potei'itial being variable or not as desired. Theimpedance 18 prevents the passage of any material portion of the radiofrequency currents directly through the battery and, therefore, suchcurrents will pass through thevariable capacity 8 in the coupling of therelays. The condenser 8 is therefore in, effect in series with the platecircuit of the preceding relay.

For any given settingof the tuned impedance coupling between the relays,the capacity of the condenser 8 will be varied to such an extent as topermit of a maximum travel of energy between the relays without causinga condition of undesirable local oscillation of the relays, and byreason of the variableness of the condenser 8, this control of thetransfer of energy without oscillation may be extended to cover all thewave lengths within the range of the receiving system. Therefore, duringoperation of the system, after the proper tuning of the coupling betweenthe relays has been accomplished either by variations of the inductance10 or tuning condenser 11 or both, the condenser 8 may be varied tocontrol the amplification or transfer of energy between the relays sothat the maximum energy transfer and amplification may be obtainedwithout oscillation of the relays.

\Vhen a fixed value of inductance 10 and a variable capacity, areemployed as the tuned impedance coupling, 1 find it of advantage tocouple the condensers 8 and 11 for concomitant operation in any suitablemanner, such as by placing them both on the same shaft or mechanicallycoupling them by other suitable mechanical means.

I have found that at the higher radio frequencies obtained through adecrease in the value of the effective capacity of the condenser 11, thevalue of the effective capacity of the condenser 8 shouldcorrespondingly decrease in order to prevent local oscillation of therelays. The practical value of condenser 8 will vary somewhat with theinductance to capacity ratio of the tuned impedance, with. the grid toplate capacity of the relays, and slightly with the other constants ofthe circuits. However, in general for the broadcast wave lengths now inuse, I have found that if the condenser 11 has a maximum value of about.0005 microfarads then the condenser 8 should preferably have a capacityof approximately .0000? to .00005 inicrofarads as the maximum.

:lefcrri g to 2, the relays 5 and 6 are coupled by a tuned radiofrequency transformer 19 in read of the tuned impedance of l, and thecondenser Se corresponding to the condenser 8 of Fig. 1 is connected lns with the primary winding of the transformer 19. The source of 15 orplate one. is also connected to the primary of the transformer 19, andalso through an impedance 20 such as a esistor element to a wire orconductor 21 which connects the condenser cc to the plate of the relay5.

In the operation of this particular system as shown .1 Fig. 2, the radiofrequency currents from the plate circuit of the relay 5 will passthrough. the condenser 8a and the 1 -iinary of the transformer 19, whilea continuous potential will be impressed on the plate of the relay 5direct from the battery or source of energy 16 through the impedanceelement 20. By varying the effective capacity of the condenser 8a thetransfer of energy between the relays may be varied, so that the maximumtransfer may be obtained without oscillation of the relays. Ifoscillation occurs in the amplifying system, itmay be eliminated by anadjustment of the corn denser 8a to decrease its effective capacity.

In Fig. 3 a detector relay is coupled to radio frequency amplifyingrelays 5 and G by any suitable means such as by either an impedance ortransformer coupling, but in this particular instance, the tuningimpedance coupling is illustrated as in Fig. 1. However, the source 23of B or plate energy for supplying a continuous potential to the platesof the relays 5 and 6 is connected to the relay plates through impedanceelements 241 and 25 which are connected by a common conductor :26 to thebattery 23. In the conductor 26 1 preferably include a variableimpedance 27 such as a resistor element. This resistor element 537 isshunted by a condenser 28 of relatively l rge value which smooths outthe pulsations of current from the battery when several tubes aresupplied with plate potential from one source of energy.

In the arrangement shown in Fig. 3, the degree of amplification of theradio frequency tubes may be varied by operation of the resistor element27 which varies the potential impressed upon the plates of the radiofrequency amplifying tubes. In case different relative potentials aredesired for the plates of the two radio frequency amplifying tubes 5 and6, the resistor elements 24 and 25 may be made variable although forordinary purposes their value may be selected initially and remainunchanged. The resistor element 2? illustrates one manner of varying thepotential transmitted from the battery 23 to the plates and is intendedto be generic, it be ing understood that other equivalent meansincluding battery taps or switches for varying the potential from thebattery may be substituted within the principle and scope of theinvention. The two condensers 8 which control the oscillations of thetubes 'may be either individually adjusted as shown in Fig. 3, orcoupled for concomitant operation as by a common operating means asshown in Fig. 6 and described hereinafter.

In Fig. 4 a circuit arrangement similar to Fig. 3 is illustrated withthe exception that the resistor elements 24 and 25 of Fig. 3 arereplacedbycholrecoils24aand25a. Thechoke coils prevent the passagethrough the battery portion of the circuit of the radio frequencycurrents which are being amplified and transferred from relay to relay.The resistor element 2? in the plate circuits of the radio frequencyamplifying tubes controls the plate potential therefor in the mannerdescribed in connection with the circuit shown in Fig. 3.

In Fig. 5 a circuit arrangement somewhat similar to Fig. 3 isillustrated in which the condenser 28 in the battery circuit is omitted,and a condenser 29 may be provided in series in the antenna circuit tofurther control the input circuit.

In Fig. 6 a somewhat similar diagram is also illustrated, but having allthe condensers 8 coupled together for concomitant operation by means ofa common operating handle or the like. The condensers 8, however, areelectrically insulated from each other, but are simultaneously variablein order to simplify the number of controls required in the manipulationof the system. Preferably the common control or coupling means betweenthe two condensers 8 should have provision for the adjustment of thecondensers, relatively to one another, in order that they may beinitially set to give the maximum amplification or transfer of energy,taking into account the constants of the particular plate circuits.

In receiving systems constructed in accordance with the invention, theincoming radio signals may be amplified at their original wave lengthsby means of the relays, preferably of the thermionic tube or valve type,and with a maximum practically constant degree of amplification for allof the wave lengths within the tuning range of the amplifier, andwithout undesirable local oscillations, merely by the adjustment of thecondensers 8 or 8a.

In referring to relays and thermionic valves, I intend to includedevices having the functions specified, such as the well knownthree-electrode vacuum tube or audion and equivalents thereof.

In all of the circuits which have been described and illustrated, itwill be understood that any number of radio frequency amplifying stagesmay be coupled by an obvious eX- pansion of the system, and that variouschanges in the details which have been herein described and illustratedin order to ex plain the nature of the invention, may be made by thoseskilled in the art within the principle and scope of the invention asexpressed in the appended claims.

I claim 1. In a radio signaling system, a plurality of three-electrodethermionic relays, plate circuits and grid circuits associatedtherewith, an adjustable tuning means comprising a fixed inductance anda variable condenser cooperating with said grid circuit, an impedanceassociated with said plate circuit, and separated from said gridcircuit, a variable condenser connected between said plate circuit andsaid grid circuit, and means comprising a mechanical connection betweensaid tuning condenser and said variable con denser for causing thesimultaneous actuation thereof, such that said variable con denser isreduced in value as said tuning condenser is adjusted for a higheroscillation frequency.

2. A radio receiving system comprising a plurality of three-electrodethermionic relays having plate and grid circuits, means comprising acoupling transformer associated between conjugate plate and gridcircuits, means comprising av variable condenser for tuning thesecondary of said coupling transformer, means comprising an impedancefor the conveyance of direct current from said plate circuit, theprimary of said coupling transformer being connected sub stantially inparallel with said impedance, and a. variable condenser connected inseries with said primary for the adjustable controlling of the amount ofradio frequency energy passed to said coupling transformer.

3. A radio receiving system comprising a plurality of three-electrodethermionic relays having plate and grid circuits, means comprising acoupling transformer associated between conjugate plate and gridcircuits, means comprising a variable condenser for tuning the secondaryof said coupling transformer, means comprising an impedance for theconveyance of direct current from said plate circuit, the primary ofsaid coupling transformer being connected substantially in parallel withsaid impedance, 9. variable condenser connected in series with saidprimary for the adjustable controlling of the amount of radio frequencyenergy passed to said coupling transformer, and means comprising amechanical connection between said tuning condenser and said variablecondenser for reducing the effective value thereof when said couplingtransformer secondary is tuned to a higher frequency.

4. A radio signalling system comprising in combination a first amplifierdevice having an anode, a cathode and a control electrode, a secondamplifier, variable means to tune said first amplifier to a desiredsignal, variable means to couple said first amplifier to said secondamplifier, said first mentioned means, said last mentioned means, saidcathode and said anode being connected in series, and means forsimultaneously varying said tuning means and said coupling means.

5. In a radio signalling system employing a plurality of amplifiersconnected in cascade, means comprising a variablecondenser connected toone of said amplifiers of such a capacity range to tune the same to anydesired frequency of a predetermined frequency range, and means toprevent said tube from going into oscillation, said means comprising avariable condenser having a range of smaller capacities than thecapacities of said first named condenser for controlling the amount ofenergy transferred to said first mentioned amplifier from a precedingamplifier.

6. A tuned radio frequency amplifying system comprising means forcoupling the plate circuit of one tube with the grid circuit of asucceeding tube and equalizing the transfer of energy between saidcircuits at all frequencies, said grid circuit having manual- 1yadjustable tuning means, said equalizing means comprising a manuallyadjustable condenser, and means whereby manual adjustment of said tuningmeans will automatically cause adjustment of said adjustable condenserto equalize the transfer of energy at all frequencies.

T. A tuned radio frequency amplifying system comprising means forcoupling the plate circuit of one tube with the grid circuit of asucceeding tube and equalizing the transfer of energy between saidcircuits at all frequencies, said grid circuit having manuallyadjustable tuning means, and said equalizing means comprising a manuallyadjustable condenser, and means whereby manual adjustment of said tuningmeans will cause adjustment of said equalizing condenser to equalize thetransfer of energy at all frequencies, the plate supply circuit beingprovided with a high impedance to restrict the escape of high frequencyenergy in the plate supply to thereby increase the effect of the highfrequency energy on the equalizing condenser.

8. In a radio signalling system employing a plurality of space dischargeamplifiers each thereof having grid circuits and anode circuits, acircuit including a tuning condenser in the grid circuit of one of saidamplifiers and means for coupling the anode circuit of another of saidamplifiers to said grid circuit comprising a condenser having a capacityof the order of one tenth the capacity of said tuning condenser.

9. In a radio signalling system employing a plurality of space dischargeamplifiers each thereof having grid circuits and anode circuits, acircuit including an inductance and a variable tuning condenser in thegrid circuit of one of said amplifiers, means for coupling the anodecircuit of another of said amplifiers said grid circuit comprising avariable condenser having a capacity substantially smaller than saidtuning condenser and a single means for simultaneously varying both saidcondensers.

i0. In a radio signalling system employing a plurality of spacedischarge devices eacn thereof having grid circuits and anode circuits.a circuit including a tuning condenser in the grid circuit of one ofsaid devices for tuning said grid circuit to any one of a range offrequencies. and means for coupling the anode circuit of another of saiddevices to said grid circuit comprising a condenser whose capacity is ofthe order of magnitude of the capacity of said tuning condenser in thevicinity of the point where said tuning condenser is adjusted to tunesaid grid circuit to the highest frequency of said range of frequencies.

In witness whereof, I hereunto subscribe my signature.

JOHN M. AVERY.

